Semiconductor devices include doping regions which need to be contacted, usually by metal layers. In many applications, aluminium or an aluminium alloy is used for the metal layers due to the low ohmic resistance of aluminium and the good contact resistance to semiconductors. However, the interface between the aluminium metal layer and the semiconductor substrate is prone to the formation of spikes. Such spikes form during annealing which is typically carried out after deposition of the aluminium metal layer, for example in a temperature range between 350° C. and 450° C. Spikes formed and extending into the semiconductor substrate may cause current filaments which could destroy the semiconductor device. Furthermore, spikes extending rather deep into the semiconductor substrate may reach pn-junctions or doping regions so that short circuits are generated.
One attempt to reduce generation of spikes is to lower the annealing temperature. This is, however, only possible in limited cases. Another attempt is the formation of a barrier layer between the semiconductor substrate and the metal layer. Such a barrier layer needs to be defect-free to function as barrier layer. Otherwise the barrier layer even enhances spike generation. Furthermore, barrier layers may affect the contact resistance between the metal layer and the semiconductor substrate.
In view of the above, there is a need for improvement.